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A Audi A6L 2.0T car with a mileage of about 73 thousand km in 2011. User response: after the speed of the vehicle exceeds 120km/h, the engine is seriously jitter. Each cylinder has different degrees of cylinder phenomenon, and the number of jitter of each cylinder has little difference. There is no law to follow. At the same time, the engine fault light is lit. But after the ignition switch is closed, the vehicle can start normally. If the vehicle is running at low speed (below 100km/h), the vehicle is all right. According to the owner's description, the frequency of vehicle malfunction is very high, and there are 8 serious jitter phenomena in the 10 high speed running. The car has been inspected many times at other repair plants. The result of the inspection is that the owner is changed to replace the turbocharger assembly. Fault diagnosis: 1. connection diagnostic instrument. The meaning of the fault code is: the turbocharger and the throttle connection error, check the environment conditions, the speed is about 140km/h, the engine speed is about 3800r/min. According to the test result of the diagnostic instrument, check the leakage of the turbocharger to the throttle air inlet pipe, and spray the air in the air inlet area when the vehicle is started. Carburetor cleaning agent to see if there is obvious jump momentum change in engine speed. 2. check whether there is leakage. As a result of long maintenance of this vehicle, I check the leakage of turbocharger to the throttle, and summarize a set of methods, which is to remove the air filter in the case of vehicle starting, and then completely block the air inlet of the air flow meter with the hand. After a period of time, there is no change in the vacuum of the feeling engine. The vacuum is getting smaller and smaller, that is, there is a leak somewhere in the middle; if there is no change in the strength of the vacuum, it means there is no leakage. The former method of operation is to disassemble the front bars and check the components one by one, which is time-consuming, laborious and laborious. After many tests, it was found that the components were not leaked. And when the vehicle starts, spray the carburetor cleaning agent into the intake area, the engine speed has not changed, and also shows that there is no leakage parts. 3. at this time, the maintenance is in a stalemate. Is it really as if the owner said that turbocharger must be replaced? Replacing turbochargers is a relatively big maintenance project. A careful analysis of the connection of the various interfaces of the turbocharger: the newly examined pressurized pipeline is only a connecting system of the turbocharger to the intake area, which is used to increase the pressure of the air. The turbocharger also has a smaller pipe connection with the cylinder cover cover, and the cylinder cover is connected to the throttle through a pressure regulating valve. The connection of the pipe is that when the intake manifold is pressurized, the one-way valve in the pressure regulating valve housing is closed, and the channeling of the crankcase through a channel of the cylinder cover is drawn to the vortex. In front of the wheel turbocharger, gas is directly introduced into the intake manifold when there is a vacuum in the intake manifold. The adjustment of this pipeline is a one-way valve in the pressure regulating valve. If the pressure regulating valve has internal damage, a large pressure pressure is formed in the intake manifold at high speed, and the crankcase waste gas in front of the turbocharger is introduced into the intake manifold and the additional intake amount is formed. . At this point the engine cylinder will be irregularly jitter. 4. after replacing the exhaust valve to test the car, the fault is eliminated. Maintenance summary: through the above two failures can be seen, the type of fault is caused by the small components, but, if the maintenance vehicles do not have a comprehensive understanding of the theoretical knowledge, there is no in-depth study of the theoretical knowledge, the failure will not be a substitute for the replacement parts, waste time, waste of energy, waste money. Comment: the author has a clear idea when removing the first fault, but if the author reads the fault code, the first time to read the data flow under each condition of the engine should be able to find the fault location immediately. As long as the data of the air flow meter at different speeds can be read, the air flow meter can be judged to be obviously lower than the normal value, because it is not only the gas clogging or the damage of the air flow meter. This fault should be a man-made fault. The analysis process is correct when the second fault is excluded, but the fault code of the "turbocharger and the throttle connection error" has been shown. It should be judged that the fault of the vehicle is caused by the gas path. By checking, since there is no "leakage" in the pipeline, combined with the phenomenon of engine jitter, the cause of the fault should be caused by "internal leakage". The author analyzes the working principle of the turbocharging system of the car and analyzes the possible cause of the failure according to the principle. It is important at one ten, and the author's strength is extraordinary.